This invention relates to a supported catalyst for oxidizing carbon monoxide, to a process for producing a supported catalyst, and to a process for oxidizing carbon monoxide using a supported catalyst according to the invention.
Carbon monoxide is a gaseous compound which is used in a large number of industrial processes, for instance in the production of methane from carbon monoxide and hydrogen. Carbon monoxide is also produced as an unwanted pollutant during incomplete combustion and is contained, for example, in exhaust gases from internal combustion engines. Finally, carbon monoxide also occurs naturally, for instance in coal mines.
Due to its toxicity, carbon monoxide should be present in inhaled air in the smallest quantities possible. A decrease in the carbon monoxide content of exhaust air from industrial plants or in inhaled air is therefore desirable and, if the content is too high, necessary. It has been known for many years that the oxidation of carbon monoxide to carbon dioxide can be accelerated catalytically. Catalysts which are active at as low a temperature as possible, for instance at ambient temperature, and remain active as far as possible in the presence of moisture are particularly advantageous, since they are highly suitable for use, for example, in rescue apparatus having an uncomplicated design. For instance, mixtures of gold and certain oxides of the metals iron, cobalt and nickel which are made as full catalysts are highly suitable. As the authors M. Haruta, T. Kobayashi, H. Sano and N. Yamada write in Chemistry Letters, pages 405 to 408, (1987), mixtures of gold and the aforementioned metal oxides, obtained by coprecipitation and calcination for four hours at temperatures of 400.degree. C., are capable of catalyzing the oxidation of carbon monoxide at ambient temperature, even in the presence of moisture for long periods.
In principle, it is certainly desirable to apply catalytically active metals to supports, particularly naturally valuable precious metals, since the catalytic activity can then be utilized more effectively. Predominantly, ceramic support materials are used, although organic materials may also be used. Polymeric organic foamed plastics as support materials have additional advantages compared to ceramic materials. For instance, they are advantageously light, and they are not susceptible to vibrations or mechanical shocks or impacts within certain limits.
However, the aforementioned authors have shown that gold, applied to a ceramic support, namely gamma-aluminum oxide, even after calcination at 200.degree. C., only developed significant catalytic activity during the oxidation of carbon monoxide at temperatures above about 100.degree. C. Both the high calcination temperature which is necessary for producing a supported catalyst and the high operating temperature of the supported catalyst needed to achieve a significant activity would lead a person skilled in the art to conclude that organic material would a priori not be considered as a support for this catalytically active material or for this purpose, namely the oxidation of carbon monoxide.